The D48 series of laser seems to be identical to the current 48 series from Synrad, however instead of taking a 30v DC input, it runs directly from 115v mains. The dimensions and overall construction appears to be identical to the current lasers, and after comparing to a more modern J48-2 laser it appears that laser resonator construction is identical, however there is an additional 30v power supply crammed inside of the pocket which houses the RF generators.
The warning labels
Power meter reading of a tube with a dead power supply (power went back up to about 28w with the fixes below), and a piece of plastic I cut out freehand:
My experience has shown that the DC power supplies are relatively prone to failure, of the 2 D48 series tubes I have seen both of them had a dead DC supply board, but working RF generator boards/laser tubes. Luckily, there is a simple fix, just remove the small red wire connecting the DC supply (there is a convenient screw terminal connector already there) and connect it to an external 30v DC supply, like the ones designed for a normal J48 series tube, or in my case a stack of 3 ATX type computer supplies in series (12+12+5v = 29v which is within spec). Do watch out for radiated RF emissions, or I suspect there will be some angry radio operators in your area! I just used the original ferrite beads and feed-through capacitors that were used for the 115v lines and so far everything seems to be working OK.
Additionally, on one of my tubes the controller board (green circuit board in the middle) was shot, and was turning both of the RF generators on regardless of the input signal--which was fine for general burning things but was a problem for use in a laser cutter. I did a little bit of debugging of the original board, but eventually gave up and built my own, which is essentially a optocoupler and 2 darlington transistors to control power to each of the RF generators (the design was based off the original controller, however I did not implement the thermal overheat protection).
Original driver board:
There is a wealth of information about these lasers at Sam's laser FAQ, and at Synrad's website. If you still have questionsI can be contacted at contact@krazerlasers.com